If you use photos on your web pages at all then you’ll have to make them crawlable. The search engines do not crawl photo images. It doesn’t matter if they are .jpg, .gif, or .tiff. They won’t get crawled. So you’ll have to come up with a way to tell the search engines what the photos are about. That’s what your alt tag is for.
The alt tags acts as a sort of description for the photo. It is a text description that should incorporate your keyword so that the search engine knows what the photo is about but also so that you can get another instance of your keyword on your page.
Of course, the above tag is sans the < and the >, but this is what your photo tag looks like.
The first element of the photo tag is img src. This tells the search engines where the original photo is located or where to find the photo. It pinpoints the exact location of the photo image right down to the file. Next, the alt= gives the photo a name or description. The search engines crawl that description and will index the photo according to that description, but they are also looking for an important keyword. If they find one then you get points for that. The align tag simply tells the Internet bunny where to place your photo on the page. It could be aligned right, top, bottom, or you could center the photo even. Whatever you do with your photos, don’t leave off the alt tag. Next to the img src, it’s the most important part of the photo tag.